The Period Properties dialog (screenshot below) appears when you click the Template Behavior | Closed Mode command of the Period template's context menu.
The dialog enables you to specify an Instant, Duration, or Forever value of the Period. Select the Period property you want to define (Instant, Duration, or Forever) by clicking its radio button. To enter a time value for an Instant or Duration, check the Enter time check box. Then select or enter the date (and time). Enter timezone information if this is required. Click OK when done. The Period elements that match the property defined in this dialog will be returned.
You can use the closed-mode template to display aspects of the Period, such as the Period Start (by using the Period's aspect value templates), or to select instance-document facts that contain the defined period. The screenshot below shows both types of use.